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W. A. WQOD Y COMPOSITE PISTON Filed Sept. '7, 1926 April 2, 1929.

Patented pr.- 2", l 29.

UNITED STATES PATENT OFFICE.

WALTER A. WOOD, 0F DETROIT, MICHIGAN, ASSIGNOR TO GENERAL MOTORS RE- SEARCH CORPORATION, OF DETROIT, MICHIGAN, A. CORPORATION OF DELAWARE.

COMPOSITE PISTON.

Application filed September 7, 1926. Serial No. 134,045.

This invention relates to pistons, particularly that type generally employed in internal combustion engines.

A light weight piston in an explosive engine has been 'found to be highly desirable, in that 'it reduces the weight of reciprocating parts, pern'iitting quicker acceleration, greater speed and ilexibility, and since the bearing pressure is low the bearings are long lived, 'friction is reduced, and consequently oil consumpti on lowered.

In order to produce a piston that will be light in weight yet oit utmost strength, aluminum metal or an aluininmn alloy has been employed. Aluminum has a high factor or coefficient of expansion, but it cools quicker than cast iron or steel. its great heat conductivity lessens carbon deposits on. the piston head and they are easily removed. l3ecause of its high expansion, however, an all aluminum piston becomes imp racticable since if its clearance in the cylinder is made eXact, the expansion under heat results in binding or sticking of the piston in the cylinder, while on the other hand if clearance is not exact the piston slaps against the sides of the cylinder when cold and the clearance allows raw gasoline to seep into the crankcasc to dilute the lubricating oil. On the other hand, cast iron pistons are much heavier but they do not have the great degree of expansion so that a close running lit may be had without either slap or binding. Y

rlhe object of the present invention is to provide a composite piston, which will combine the desirable characteristics oi both aluminum and cast iron pistons, without their disadvantages.

In the drawings, wherein is illustrated the preferred, but not necessarily the only embodiment oi the invention, Figure l is a vertical sectional view a piston embodying the invention taken on line l-l oit Figure 2.

Figure 2 is a vertical cross sectional view on line 2 2 of Figure l.

Figure 3 is a section on line 3.3 ol F igure l.

Figure 4 is a section on line 4%4 ot Figure i.

Fig. 5 is a Vertical section showing` the inn vention embodied in another type of piston.

The piston comprises a head l, and a barrel having an inner and outer wall, which consists respectively ci a skirt portion 2 formed integral with the head l, and a continuous seamless sleeve or shell 3 closely fitted on and surrounding the skirt. The integral head and skirt are preferably formed 0f aluminum or other light weight metal having similar characteristics. Grooves 4 are provided in the head for locating the customary sealing piston rings to make the piston gastight. rlhe shell or sleeve 3, which may be fa cned by rivets or otherwise to the skirt, to ns a working face or guide for the piston, as it reciprocates within a cylinder. It is preferably formed from steel or other ferrous metal which has a much lower co-eliicient oit expansion than the aluminum head and skirt. In case an oil ring is used with the piston, a groove G maybe provided in the skirt which then separates the shell 3 into two bands-as shown.

Projecting downwardly from the head l, but spaced from the skirt portion 2, are a pair of bosses 7H-7, with suitable reeni'orcing ribs 8 and 9, which bosses 7 7 are bored to receive a bearing bushing for mounting the wrist pin of a connecting rod. Openings in opposite sides of the skirt 2 and shell 3 register with thc openings in the wrist pin bosses for 'facilit ating` the attachment.

Since cast iron or steel has a co-ellicient of expansion ot' only about one half that of aluminum, the clearance between the cylinder and cast iron piston may be comparatively small as compared with aluminum pistons. lVith the present composite piston, the clearance space will be that oi a cast iron piston due to the steel sleeve. The head l, however, will be a 'few thousandths o', an inch smaller in diameter than the sleeve 3 to permit its eXpansion, but since the piston will be guided by the sleeve, the smaller diameter of the head will not result in slap. In order to compensate for the difference in co-eliicients of expansion between the sleeve and a skirt, the body of the ski rt is cut or slotted. One or more such slots may be employed, the desirable arrangement lieiirg the use ot' about siX equally spaced lougitrulinal slots l0 distributed around the skirt 2, In order not to weaken the body of the skirt the slots do not extend trom end to end, but terminate at spaced points from the top and bottom extremities. The slots, therefore, permit circumferential expansion of the skirt, vthat is, the expansion moves toward and fills the slots instead of radially or outwardly, whereby there in no forcible ont-- ward expandingl p reeffiure exerted on the Sheet metnl :fdeeve il. To take cere oli' expansion oi the skirt at the upper and lower terminale ol*l the slots where there will be .little or no eirenmstzrntinl expnnnio'n, the end portions or top and bottom ot the eizirt are pe'riiidiernlly beveled or tapered inwardly :is at ll und i2, leavingv small, speeee between the shell l :ind skirt 2 into which tl a skirt may expand radially. The tapers entend from earch Vtop :ind bottom extremity to pointe overlirpping;` the elet terminale. Radial or outward expennion will increase the diameter oit the beveled ends; only a. few thouearulthe` of an inch and an ir- Waa'd taper of about .lllh will be eullieient. 'lhus the Slots permit the mujer portion ol the skirt to expand cireumil'erentially, witlu'nit mnterinlly wealte'uiin;l the f:l irt wull hermine of the cloned ende, whili` noch closed end portions are permitteifl a. radial eximnsion by reducingI the diameter 'tor n Small extent at euch ends, providing clearance between the skirt :md shell.

The construction ol' Figure 5 showtv Vthe application oi the invention to n. shorter length piston which does not have en oil groove in the skirt portion and the sheet melinl Sleeve is undivided. 'lhe arrangement is; otherwise the mine an that beilfore deneribei l.

l't will thus be eeen that the advui'itaejee olf :in alumimun pieton and n. east iron piston nre combined into one (.:ompoeite piston without the diendvztiilnziggiifq oi either. 'lhe body being` of ligrl'it yet strong,` nntterinl, permits high compression and flexibility oil4I operation. Carbon depossitn ire leon likely to form on the aluminum heed :md `the large uren. ot aluini mun permi te quick cooling o'l 'the piston. lhe thin sheet metal sleeve given n. Smooth Workingr surlnce. to the pieton, which muy be lil'- ted cloeel y Within the eyliinler, obvintinn' Slap during cold engine conditions or binding when the engine becomes heated.

l/Jhile the construction and nrraiu lment oi ports have been deecribed more or lese specifically, it is to be understood that olni'ioun modifications may be made as come within the scope o'l' the appended clniino.

I'litvingr described my invention, l eleim l.. il. piston comprising` n head ilorn'ied with ring grooves in the ileripherul portion there-- of, a. cylindrical skirt dependingvfrom Said heard and forming :i contini'iation oii Suid peripheral grooifed portion, und having; a .fslot extending;` throughout :in interinei'linte portion :in d termimrtinn short oli the ende thereo'li, and n sleeve formed oi a. metal lnrviiug` :t leaner co-eliieient oil' expansion than 'the nli'irli, closely litted around Said skirt und endim;` short of the `grooved periphernl portion oiE the heed to provide n. continlmue unbroken working nur'lnee 'tor the skirt.

2. A pieton. eomprieinn' :t head. n, eyliiulril eel ski rt, integral with und dejiendinn iroin merma sind heed, ay continuous unbroken sleeve closely litted about Suid Skirt and bei ne' :termed o'lf e motel havingl n lower etrellicieiit of expansion than sind skirt, Said eltirt haring); poi tiene cut :may intern'iediafte :ite ende to provide openings into which the metal oil the elfi rt nuty move eircun'iiierentially to compensate lier the relative dill'erential oit' enpnneion between the skirt and sleeve.

3. A piston comln'ieinl,y :L heed, a. eylindricai Shirt, .integral wi th and dependi 'from said head, at contimioue unlnrolren sleeve cloeely titled about Seid skirt and lfieingr ilbrmed o'lj ny metal hnvinig :i lower eo-ellicient oli elpansion thzm Said skirt, seid ski rt having' portions eut away interim-dinte its ends to provide o'ieningn into which the metal oili' the Skirt may move circumierentiully to Compeneate :lor the relative diliferential oif expnnnion between the Skirt and sleeve, and iiinl'on pin bosses; czirried by seid heed and extending, into, but having no eoi'inection with the skirt Ll. il pieton coinprininn` a. heed and n. skirt bowing:y n. relatively high ez'iei'licient oi? expennion, eaid ski rt being,Y provided with filete cxtemlingg,` throughout u portion of the Skirt inH i'erinediate the endn thereof, and :t Continuous; unbroken. eleove hui/'ing e relatively low coeilicient oi' expansion cloeely Iitted on .ea/id skirt.

5. The pieton sin claimed in claim el, und pieton pin bonnen carried by seid head, which project within but are independent oi Said skirt.

G. A pieton comprising n head formed With rung` grooves in the peripheral wall thereof, n cylindricol skirt depending' from md 1to1-ne ing :i continuation oi" said well, pieton pin bosses depending from seid hond and located Within but having no connection with said skirt, a sleeve fitted on Said skirt and having a lower co-etiicient ol. expansion than said skirt, end means to compensate :lier the relai tive diilerentiel ol expansion between the skirt and sleeve.

"i. A. piston including n. head and eliirtol light weight metal having a high factor of exilnmeion, e sheet metal sleeve of a smaller itector of expansion litted over the skirt to :it` lord o Working surface, the skirt being' inwnrdly tapered at the margins of the sleeve affordingclearance spece therebetween, and having a out extending thru the body of the Skirt to points intermediate the tapered por tions to aeeonnnodnte the high :lector of expaneion oilE the nlfirt within the sleeve.

8. il pieton including` :i head and Skirt of high lient conductivity, the diameter oli the Skirt beine' reduced at the top .find bottom oit its body md the nliirt body l'iaving),` :i plurality oi" slots extending thru-ont Aits length, :1nd n, .Cseumlens sleeve oli uniform diameter thru-out oi low heat Conductivity fitting over the Skirt 1with its ends :it the top and bottom oi" the skirt whereby the expansion under heat moves the skirt into the reduced top and bottoni and slotted portions Without affecting the sleeve.

9. A piston including a Working surface consisting of a thin sheet metal shell having a relatively low co-eilicient of expansion and a light weight head and skirt having a high eoeiiicient oi' expansion on wliich'skirt said shell is fitted, the end portions of the skirt being of smaller diameter than the remainder of the skirt body whereby radial expansion at the ends will not aliect the shell, the remainder oit the skirt body having a plurality of spaced openings permitting circumferential expansion oi? the skirt body.

l0. A piston including a working surface consisting olf a thin sheet metal shell having a low :factor ot' expansion and a light Weight integral head and skirt having a high factor of expansion, on Which skirt said shell is carried, the difference in expansion being compensated lor by providing slots extending thruout the length oit the skirt body terminating away from the skirt extremities to permit circumferential expansion of the major portion of the skirt body, and 'further providing peripheral inwardly beveled end portions on the skirt body overlapping the slot terminals atording spaces between the shell and skirt at their respective ends to permit radial expansion Without affecting the shell.

11. A piston including a light Weight head and integra-l slotted skirt With 'depressions at its top and bottom, having a high factor oi heat conductivity7 and a sheet metal sleeve of a low factor of heat conductivity surrounding the body of the slotted skirt With its ends located over the top and bottom depressions, whereby under heat the slots permit the skirt body to expand circuinferentially and the depressions permit radial expansion without affecting the sleeve.

12. A piston including a head and skirt of light metal having a high co-eiicient of eX- pa nsion, a sheet metal sleeve surrounding the skirt and forming a part thereof, having a lesser co-effieient of expansion, the top and bottom portions of skirt being tapered at the ends of the sleeve, and the skirt body having a plurality of longitudinal slots overlapping and terminating intermediate the respective tapered portions, such tapered portions and slots acting conjointly to compensate for the difference in co-eliicients in respectively permitting radial and circiunferential eXpansion of the skirt Without affecting the sleeve.

In testimony whereof I aiiix my signature.

WALTER A.' Woon. 

